This invention relates to a mechanism for a positioner and to a positioner having such a mechanism, more especially to a multi-axis positioning mechanism.
Positioners have many scientific and industrial applications.
One application, for example, is the positioning of optical fibres relative to each other, relative to waveguides, laser diodes, detectors etc, prior to testing and joining. This type of positioning has to be very precise, typically of sub-micron precision, and is commonplace in research and production facilities in the telecommunications industry.
Another application is for positioning optical or non-optical components, such as mirrors, lenses or samples beneath microscopes.
There are two main types of precision positioning stage, those based on bearings and those based on flexure hinges. The simplest form of both types of design produce linear motion, so called x-positioners. Both types of design can however be adapted to produce rotary motion with additional linkages and the like, so called .theta.-positioners.
Many applications require not one, but several, axes of motion. This is obtained by stacking several stages. For example, bolting the top plate of one bearing stage to the base of another linear stage so that the respective positioning axes are at right angles to each other will produce a two-axis positioner, or so-called xy-positioner. Moreover, by then bolting an L-bracket onto the top-plate of the y-stage and a further bearing stage onto the upright of the L-bracket, a three-axis positioner, or so-called xyz-positioner, is produced.
Sometimes multi-axis positioners are supplied as integrated units. For example, in an xy-positioner, the top plate of the x-stage can also serve as the base plate of the y-stage, to reduce size and weight.
Flexure stages can also be nested in various ways to make them more compact.
However, the integration of parts in this way does not affect the basic principle of operation which is to use a number of similar mechanisms connected serially.
There are however several drawbacks to the use of a series of single axis mechanisms for multi-axis positioners:
1. The complexity and cost tends to increase with the number of axes. PA1 2. The mass of moving parts increases with the number of axes, making the positioner slower to respond and more susceptible to ambient vibrations. PA1 3. The force of adjusting a micrometer (other than that of the first stage) is transmitted through the preceding stages, causing disturbance to the position of the stages. PA1 4. The stiffness of the positioner decreases as the number of axes increases. PA1 1. Low mass of moving parts--better response time, more resistance to ambient vibrations. PA1 2. Adjusting a micrometer, or other actuator, for one axis does not result in force being transmitted through the mechanics of the stage and disturbing the positions set by the or each other stage. PA1 3. Greater stiffness resulting from the parallel rather than serial action of the linkages. PA1 4. Because there are fewer parts in series, lost motion among adjacent parts is minimized and the overall precision is improved. PA1 5. Simpler design, lower cost.